An "adjuvant" is a substance that itself is often biologically inactive but which, in conjunction with a given antigen, enhances its antigenic capabilities. Adjuvants have been used experimentally in animals for studies on the immune system and in vaccines for improvement of immunological responses, as measured by antibody titres. The enhancing effects have, in many instances, been confirmed by application to humans.
Prior art adjuvants range in type from simple inorganic materials, such as, aluminum phosphate, to complex mixtures, such as, Freund's adjuvant, which is a homogenate of oil, detergent and killed tubercle bacilli.
One advantage of the use of adjuvants in vaccines lies in the fact that the same degree of antibody response can be achieved with a smaller amount of antigen. This advantage is demonstrated in the case of an antigen which must be used at a dosage where marked primary reactivity is shown in order to induce a suitable antibody level. Adjuvants are particularly useful in cases where the antigen alone does not stimulate high levels of antibody. A main function of an adjuvant is to raise the antibody response to levels which will ensure protection against an infectious disease.
Any material used as an adjuvant in vaccines should be non-toxic, relatively easily metabolized and produce little or no skin reaction at the injection site.